Process for removal of sulphuric acid compounds from hydrocarbon oils



PatentedMar.1 2,1940 Vii-"i I 2,193,417 r raocsss FOR REMOVAL OF SULPHURIC 1 ooMroUNps mom HYDROCARBON William Patrick Gage, Deer Park, Tex., assignor to Shell Development Company, San Francisco,

Calif., a corporation of Delaware No Drawing. Application August 2,1938,

Serial No. 222,633

,- I 2 Claims. (01. 196- 1 1) This invention relates to an improvement in pressures suiiicient to keep water in the liquid the treatment of hydrocarbon oilscontain'ing oil phase at these'te'mperatures, are required to effect soluble substantially neutral sulphuric acid comsuch hydrolysis. 'This method is also subject to pounds such as alkyl sulphates, with aqueoussocorrosion difficulties because of the inherent lib- '5 lutions of alkali metal hydroxides or alkali earth eration of sulphuric acid. Therefore, where corrnetal hydroxides under hydrolyzing conditions rosion: resistant equipment is not available, the fertile purpose of removing such sulphuric acid usual practice has been to carry out the hydrolycompounds, and more particularly is concerned sisin the presenceofa minimum amount of a with the use of said alkali metal hydroxides constrong base sufficient at least to neutralize the c in i 'taining small amounts of an-oil soluble base to liberated acid. While caustic alkalis tend to pre- 10 achieve said purpose. vent corrosion, theyoften materially reduce the When contacting hydrocarbon oils with sul rate of hydrolysis. For the last reason and also phuric acid, as, for example, when treating to reduce the cost of the treatment, large excracked hydrocarbon distillates or polymerizing cesses of base over this minimum amount have in olefines with sulphuric acid, substantiallyv neugeneral been avoided. l5

tral, oil soluble sulphuric acid compounds may Of thevarious bases availabla sodiuin or calbe formed, such as sulphuric acid esters, sulciurn hydroxides are usually employed; because phonic acid esters and possibly other compounds they are the least expensive, and strong bases of unknown composition. These compounds deare generally considered to be more efiective in q 2 compose in contact with caustic alkali at elepre'venting jacid corrosion than weakerbases. vatecl temperatures with formation of acids, at However, other'strong bases, such as the remainleast a portion of which are sulphuric and suling alkali metal hydroxides, ammonia, quaterphurous acids. nary amznoniwn bases, etc., are operative, a1-. 7 The term sulphuric acid compounds as herein though their cost is very much higher than that '25 used refers to oil soluble substantially neutral of sodium-orcalcium hydroxides' compounds which are formed by reaction 'be- Now I have found that frequently serious cortween sulphuric acid and hydrocarbons and lesion-results when'hydrolyzing hydrocarbon oils which are capable of liberating acids under hycontaining sulphuric acid compounds even inzthe drolyzing conditions. Inthe following disclosure, presence of an arnountof caustic soda or lime 3' 1' shall repeatedly refer to hydrolysis of the. sulsubstantially/in excess of that required to neu-- phuric acid compounds. While it is knownthat tralize the potentially liberated sulphuric acid. at least some of the sulphuric acid compounw An investigation into this problem has disclosed do undergo actual hydrolysis under the condi that thereappears to be a relation between the tions whichlmaintain, other sulphuric acid comintensity of corrosion and the intensity of agi- 3 pounds may decompose to yield acids by difiertation during hydrolysis, corrosion. decreasing as 1 ent mechanisms the nature of which is not defi' a ritation becomes more violent. This observation nitely known. It shall however be understood has'led me to believe that the corrosion which that w hereinafter Speaking f yd ysis. takes place in spite of an excess OfCEtllEiillC soda hydr ly ins, t reactions other tha ru hyor lime is caused y liberated sulphuric or sula drolysis may take place in d t to u hyphonic acids which are iinmediatel diluted but O Y fl the hydlolyzing conditions'herenot immediately neutralized I without effective aftel' describedagitation, or by acids which are'sol'ubl'e in the It is known that sulphuric acid compounds oil phase and whiohare removedtherefrczn only i. such as alkyl sulphates can be hydrolyzed with gradually by the oil insoluble aqueous caustic Water at elevated temperatures either in the alkali. The more intense the mixing, the quicker 45 absence of active chemicals, or with the aid of the acids absorbed by the c'austic Soda and dilute mineral acids or alkalis. Acids in general h corrosion takesplaca since the decom a z iii ggg i z g z ggggg iti ggz gg position from neutral sulphuric acid compounds co 'rosion difiiculties. l lydrolysis of sulphuric P r acids requires m t be contained r acid compounds contained in mineral oils with m the durmg thls m m at least a water, e. g. as the sole reagent is described in the Small of unneutlia'h-zed aclds Whlch are Retailliau Patent 2,088,216; and according to this e p sible for the corrosion. Therefore, as long patent temperatures above the normal boiling as there'ls a pply neutral Su phu c acld point of water and preferably above 250 F., and compounds, corrosion must be expectedto proble base.

ceed until all of them have been hydrolyzed and have disappeared.

In order to shorten the time lag which exists between the formation of corrosive acids and their conversion to substantially non-corrosive salts, I have added small amounts of an oil soluble base to the reaction mixture, which amounts were just sufiicient to neutralize the free acids temporarily contained in the oil phase. The presence of the base in the oil has the effect of causing substantially instantaneous neutralization of the acids, whereby corrosion is effectively checked. When thereafter the salt of the oil soluble base and the monoalkyl sulphate comes in contact with the aqueous solution of caustic soda or lime, the latter displaces the oil solu- As a result, the oil soluble base is liberated and remains in the oil ready to neutralize further amounts of corrosive acids formed subsequently.

Time is required for the exchange of bases and transfer of the acids from the oil to the aqueous phase, and in general the rate of exchange increases with the violence of agitation. However, the influence of the intensity of agitation becomes less significant, if the salts of the oil soluble base with the acids are soluble in both the aqueous and oily phases. Under these conditions, the exchange may be quite rapid even'when m1ldly agitating, and the amount of oil soluble base which is tied up by monoalkyl sulphates, is in general smaller than if its salt were substantially insoluble in the aqueous phase.

Suitable oil soluble bases are those which are sufilciently alkaline to form with sulphuric acid substantially non-corrosive salts such as ammonia and those of the primary, secondary and tertiary amino bases, the emulsifying powers of which are insufi'iciently strongto produce substantially permanent emulsions of the hydrocarbons and the aqueous solution. Such emulsions, if allowed to form, are likely to cause serious difliculties. For example, the alkanolamines, such as triethanolamine, though operative, may cause difiiculties because of their intense emulsification powers.

Ammonia is particularly useful because it is relatively inexpensive and its salts with many of the monoalkyl sulphates are soluble in both the oil and aqueous phases. Moreover, it is not an emulsifying agent.

The minimum amounts of oil soluble base required successfully to prevent all danger of corrosion varies with the conditions such as intensity of agitation, solubility of the base or its sulphate salts in the aqueous phase, etc., as previously pointed out, and therefore cannot be stated definitely. When using ammonia, the amounts required are in general less than about 20% and usually not more than about 10% of the total amount of base necessary to neutralize the sulphuric acid potentially liberated from the alkyl sulphates in the course of the hydrolysis. Amounts of the oil soluble base greatly in excess of the minimum required completely to prevent corrosion are of no material benefit, and on the contrary raise the cost of the treatment and also the danger of producing harmful emulsions.

In order to accelerate the hydrolysis, I usually employ superatmospheric pressures and temperatures in excess of the normal boiling point of water.

The following example illustrates the advantages of my process:

Hydrocarbon polymers produced by polymerization of olefines by the hot sulphuric acid polymerization process described by McAllister in A. P. I. Proceedings, volume 18, section 3, pages 78-83, November 1937, containing about .4% sulphuric acid compounds calculated as H2804 were hydrolyzed in a steel pressure tank 9 x 40' equipped with open and closed steam coils. A charge of 210 to 220 bbls. of the polymers was pumped through a heater into the hydrolyzing tank, and an amount of aqueous caustic solution of 10 to 15 B. slightly in excess of that required to neutralize all potentially liberated sulphuric acid was added thereto and passed into the tank. The contents'of the tank were agitated under pressure of about 190 lbs. per sq. in. with open steam for about three hours, whereby a temperature of about 300 F. was maintained and the average concentration of the caustic soda reduced to about 1% by the condensed steam. At the end of this period, the polymers were substantially free from sulphuric acid compounds, and a slight excess of free caustic soda remained. The entire charge was then withdrawn and the above procedure was repeated with a new batch of polymers.

In spite of the excess of caustic soda, serious corrosion resulted within a short time. Increasing the excess of soda did not abate the corrosion. The difiiculty, however, was completely overcome by adding to the mixture of polymers and caustic soda an amount of ammonia equal to about 10% of the caustic soda charged, the ammonia being introduced into the hydrolyzing tank together with the caustic soda.

I claim as my invention:

1. In the process of removing substantially neutral oil-soluble sulphuric acid compounds contained in a hydrocarbon oil by treating same with an aqueous solution of a caustic alkali selected from the group consisting of alkali metal hydroxides and alkali earth metal hydroxides in an amount at least equivalent to the acid potentially liberated from said sulphuric acid compounds under elevated temperature and pressure conditions to hydrolyze said compounds and to produce acids which are neutralized by the caustic alkili, the improvement comprising treating said hydrocarbon oil with said caustic alkali in the presence of an added small amount of ammonia said amount being equal to less than 20% of the equivalent of said potentially liberated acids.

2. The process of claim 1 in which the amount of ammonia equals less than 10% of the equivalent amount of potentially liberated acids.

WILLIAM PATRICK GAGE. 

